The present invention relates to a cuvette for use in an optical evaluation instrument and a device for positioning the cuvette along a linear path in the instrument.
Optical clinical laboratory instruments that evaluate a biochemical reaction taking place in a reaction well of a cuvette are known. In such an instrument, the cuvette is placed in an optical path of the instrument and a light beam, which passes through the cuvette, is received by light detectors. Evaluation of the output of the light detectors reflects changes in optical characteristics along the optical path caused by the biochemical reaction taking place in the reaction well of the cuvette. Such instruments are used to perform analysis relating to, for example, hemostasis, thrombosis, infectious diseases, and the like.
In one type of known optical instrument, a plurality of cuvettes are arranged in a one-piece circular tray and rotate around a fixed center position. This type of instrument is, at best, only semi-automatic. In another known optical instrument, a linear cuvette system makes it possible to have a walk-away automatic unit with an uninterrupted supply of cuvettes. Known, commercially available instruments using a linear cuvette system use a timing belt or steel belt for driving the cuvettes along a linear path. In these systems, teeth on the timing belt mate with corresponding teeth on the cuvettes and drag the cuvettes along the linear path. There are also systems that use combinations of rotary and linear cuvette drives. The timing belt, however, does not provide accurate positioning of the cuvette because there is a variation on the length of the belt that increases with the length of the belt (i.e., the longer the belt, the greater the tolerance). The placement of a cuvette relative to a fixed point on the path changes as the cuvette moves through the system in equal increments.
Optical evaluation systems are being developed which utilize small reaction volumes, on the order of 100 microliters, in the cuvette. In such systems, the positioning requirements for the cuvette are quite severe and are not satisfied by commercially available linear cuvette systems and the traditional timing belt drive mechanisms used therefor.